1 - You see a plane in the sky and instinctively reach for your Stinger missile.
2 - You have the königgrätzer marsch as your ringtone.
3 - When walking the streets you can't help but strafe around corners, crouch behind cars and run for cover whenever you see a helicopter or low flying plane. You also regularly check windows and the horizon for snipers.
4 - When speaking to friends you say "I'm Oscar-Mike" to let them know you're on your way. And you think nothing of using the words "tango", "x-ray", "hitman-actual" and "UAV" in every day conversation.
5 - You know your kill to death ratio and weapon accuracy off the top of your head across all three Call of Duty games and have a stat trackers installed on your phone or PC. And heaven forbid anyone else ever tries to every play using your account - their life would not be worth living. In fact the game is less about having fun and more about comparing the size of your e-penis with that of your friends.